Pocket knives provide a convenient tool for cutting that may be easily carried by a user. A folding knife is a particular style of pocket knife that has a blade pivotally connected to a handle. The handle generally has a butt end opposed to a head end and a back surface opposed to a front surface. The blade pivots with respect to the head end of the handle to transition between retracted and extended positions. When retracted, a cutting edge of the blade resides inside the front surface of the handle, and the handle protects the cutting edge from inadvertent contact that might damage the cutting edge or cause personal injury. When extended, the blade extends from the head end of the handle to expose the cutting edge for use.
A manually operated folding knife requires a user to physically rotate the blade with respect to the head end of the handle to reposition the blade between the retracted and extended positions. A single action folding knife includes a spring that engages with the blade to automatically extend the blade, and the user must apply force to the blade to overcome the spring force to manually pivot the blade with respect to the head end of the handle to return the blade to the retracted position. A double action folding knife includes a spring that engages with the blade to automatically extend and retract the blade.
Folding knife designs often balance competing goals of safety with ease of operation. For example, some folding knife designs include a lock to enhance safety. The lock engages when the blade is extended and/or retracted to prevent inadvertent movement of the blade between the extended and retracted positions. The additional safety provided by the lock generally requires additional action to release the lock before repositioning the blade between the extended and retracted positions and therefore reduces the ease of operation of the folding knife. Other folding knives are non-locking to enhance ease of operation. For example, a slip joint knife is a non-locking folding knife that securely holds, but does not lock, the blade in the retracted or extended positions. A slip joint knife typically includes a cantilever or a spring bar attached to the butt end of the handle and that extends along the back surface of the handle to the head end of the handle. At the head end of the handle, the cantilever or spring bar is biased against the blade to securely hold the blade in the retracted and extended positions. To reposition the slip joint knife between the retracted and extended positions, a force is applied to the blade to overcome the force of the cantilever or spring bar against the blade.
It is desirable for a slip joint knife to operate reliably over decades of use and through thousands of cycles between the retracted and extended positions, and the material selected for the cantilever or spring bar must balance flexibility with hardness to provide the desired reliability and durability. Titanium or steel is typically used for the cantilever or spring bar because these materials possess sufficient strength and flexibility to provide the desired bias against the blade to securely hold the blade in the retracted and extended positions. However, titanium and steel are generally softer than most blades that are heat treated or hardened. As a result, repeated cycles of the blade between extended and retracted positions causes the blade to erode the surface of the titanium or steel cantilever or spring bar which adversely impacts reliable operation of knife. Eventually, the titanium or steel cantilever or spring bar must be replaced to allow the slip joint knife to operate reliably.
Therefore, the need exists for an improved folding knife that can securely hold the blade in the retracted and extended positions while also providing enhanced durability to reduce the need for repairs and maintenance.